Now to a case of major league misbehavior by a suburban little league mom convicted of stalking her son's baseball coach and his family. Her threats were chilling and anonymous and turned her victim's life into a nightmare. ABC's Deborah Roberts has the story. Reporter: If you think little league sports is all about team building, think again. Nearly every weekend, bad calls lead to bad behavior. But the mvp, most vicious parent award may very well go to the mom who secretly terrorized her son's little league coach and his family with threatening notes. You all better watch your backs. This is no joke. Reporter: It began in east meadow, New York, after the little league office received a letter accusiing the coach of giving special treatment to his son. There's another letter and another letter. And soon a special delivery to them. Two handwritten envelopes in our mailbox so I opened both. One was addressed to my son. I made it my life's goal to observe your family on a 24/7 basis. Don't be planning a vacation any time soon. You will have no home to come back to. The letter to my son was just took me down because it just said if he doesn't step back I'm going to kill him. Reporter: How frightened were your children. His initial reaction was to put down his gloves and his bat and said, you know what, dad, I don't need to play baseball anymore. Reporter: Evidence pointed to an angry parent of one of Dominic's fellow sluggers, but they would soon learn their tormenter was terrifyingly close to home. I could feel my knees starting to shake as I was standing there and I couldn't believe it. Reporter: For "Good morning America," Deborah Roberts, ABC news, New York. We're here in the social square. We wanted to hear from you. Should there be rules for parents when it comes to their behavior in little leagues and so these are some of your responses. Megan says, "Yes, especially no parents in the dugout." That's one way of going. On Facebook we heard from Angela. "No cursing, no threat, no fighting with other, good-natured smack talk is acceptable." Time for one more on Facebook from Patricia. "Yes people act like this is life or death. It's not "Hunger games." It's kids having fun. Sit down, enjoy the game or stay in your car." Tonight on "20/20" deb will share more of this little league mystery that took over a year to solve. At 10:00 P.M. Eastern, 9:00 central.

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